Precision inspection device using digital moire patterns based on monochromatic light source

Abstract

The present invention relates to a precision inspection device using a digital moiré pattern based on a monochromatic light source. By using a quasi-coherent light source based on monochromatic light, DC noise and speckle noise are minimized while maintaining appropriate coherence. Additionally, by guiding light from a point light source through an optical fiber to create uniform parallel light through a focusing lens, stray beams are effectively eliminated. Furthermore, by minimizing polarization noise in advance using a polarizer and directing it to an optical space modulator, various interference pattern light sources for forming moiré patterns can be easily obtained.

Description

Technology Field

[0001] The present invention relates to a precision inspection device, and more specifically, to a precision inspection device using a digital moiré pattern based on a monochromatic light source. Background Technology

[0002] Recently, parts and components of products mass-produced in industrial processes are becoming smaller, ranging from micro-scales to tens of nanometers.

[0003] Currently applied analog precision inspection methods based on diffraction gratings (3D AOI, 3D AXI, etc.) have limitations in precision inspection of high-step and high-precision devices. For this reason, a digital precision inspection method based on optical space modulators is being proposed.

[0004] Furthermore, while conventional diffraction grating-based moiré pattern formation methods can measure defects down to the sub-micron level, they suffer from the inconvenience of requiring the use of diffraction gratings with different spacing depending on the defect size. For this reason, although the efficiency of current 3D AOI inspection technology using digital moiré patterns is highly regarded, precise inspection of nano-scale fine defects is impossible because it fails to minimize DC noise caused by white light and noise caused by the polarization of optical space modulators. Prior art literature

[0005] (Patent Document 0001) KR 10-1613829 B1

[0006] Yu, Won-Jae, & Kang, Young-Jun, "Shape Measurement Method Using Moiré Effect," Journal of the Korean Society of Precision Engineering, Vol. 22, No. 4, April 2005. The problem to be solved

[0007] To overcome the limitations of the aforementioned conventional inspection technology, a precision inspection device using a new type of digital moiré pattern is proposed. In particular, to solve the aforementioned conventional problem, DC noise is minimized by using a monochromatic light-based quasi-coherent LED light source and a polarizer. means of solving the problem

[0008] To achieve the above objective, the precision inspection device using a digital moiré pattern according to the present invention is characterized by comprising: a light source; an optical fiber that transmits light from the light source; a point light source formed at the end of the optical fiber; a focusing lens that converts the light from the point light source into parallel light; a polarizer that polarizes the light passing through the focusing lens; an optical mirror that reflects the light polarized through the polarizer; an optical space modulator that creates an interference pattern light source digitally by incidenting the light reflected by the optical mirror; and an imaging lens that transmits the light from the interference pattern light source.

[0009] The above light source may be a monochromatic light-based quasi-coherent light source having a full width at half maximum (FWHM) of ±10 to 200 Å based on the center wavelength.

[0010] The above focusing lens may be an aspherical lens or a compound lens aligned with the above central wavelength.

[0011] The light source is an LED light source, and a band filter may be further provided between the focusing lens and the polarizer to reduce the DC noise of the LED light source.

[0012] An aperture and a beam splitter are further provided between the optical mirror and the optical space modulator, and the aperture and the beam splitter can be arranged such that light reflected from the optical mirror passes through the aperture, and only a certain amount of light passes through the beam splitter and is incident on the optical space modulator, while light from the interference pattern light source passes through the beam splitter and then passes through the imaging lens.

[0013] The above optical space modulator may modulate the incident light by 90 degrees to create the interference pattern light source. Effects of the invention

[0014] The present invention uses a quasi-coherent light source based on monochromatic light to minimize DC noise and speckle noise while maintaining appropriate coherence, and guides it into an optical fiber. The light emitted from the point light source guided into the optical fiber creates uniform parallel light through a focusing lens, thereby effectively removing edge noise caused by a planar light source, and by minimizing polarization noise in advance with a polarizer and directing it to an optical space modulator, it has the effect of easily obtaining various interference pattern light sources for forming moiré patterns. Brief explanation of the drawing

[0015] FIG. 1 is a diagram of an optical system configuration according to one embodiment of the present invention. FIG. 2 is an optical system configuration diagram showing an example in which a band filter (131) is additionally used in front of the polarizer (130) in FIG. 1. Specific details for implementing the invention

[0016] Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings.

[0017] A precision inspection device using a digital moiré pattern according to one embodiment of the present invention comprises, as referenced in FIG. 1, a light source (100); an optical fiber (111) that passes light from the light source; a point light source (110) formed at the end of the optical fiber; a focusing lens (120) that converts light from the point light source into uniform parallel light; a polarizer (130) that polarizes light passing through the focusing lens; an optical mirror (140) that reflects light polarized through the polarizer; an optical space modulator (200) that creates an interference pattern light source digitally by incidenting light reflected by the optical mirror; and an imaging lens (210) that passes light from the interference pattern light source.

[0018] Here, the light source (100) may be an LD (Laser Diode) or an LED (Light Emitting Diode). The former has the advantage of being able to be transmitted over a long distance (more than 4 meters) via optical fiber and having high coherence, but when considering the long-term use of the precision inspection device, and in the case of a coherent light source with a line width (Δλ) of less than 2 nm, it has the disadvantage of requiring a complex optical system such as a Michelson interferometer due to speckle noise problems. In the case of the latter, the distance that can be transmitted via optical fiber is short, within 4 meters (see Gye Gwang-hyeon, Son Gyeong-rak, "Study on Bidirectional Wireless Communication System Using Visible Light LED," Journal of the Korean Society of Marine Engineering Vol. 34, No. 6, pp. 852–857), but it is suitable for long-term use of the precision inspection device, and in the case of a quasi-coherent light source with a line width of about 20–40 nm, it has the advantage of having appropriate coherence and minimizing DC noise and speckle noise. Accordingly, the light source (100) is preferably a quasi-coherent light source based on monochromatic light having a Full Width at Half Maximum (FWHM) of ±10 to 200 Å based on the center wavelength, that is, a line width of 2 to 40 nm.

[0019] The optical fiber (111) is configured to receive light from a light source (100), undergo total internal reflection, and output it as a point light source (110) toward a focusing lens (120) via a predetermined path (including a curved path). By using the optical fiber (111) in this way, the quasi-coherent light source is selectively output as a point light source (110), that is, while excluding other unwanted beams. This is even more required when using an LED as the light source (100). The point light source (110) is necessary to obtain uniform parallel light through the focusing lens (120). If the light from the LED is passed directly through the focusing lens (120), it is not dependent on the point light source (110), making it difficult to obtain perfectly parallel light through the focusing lens (120).

[0020] The focusing lens (120) may be an aspherical lens or a compound lens for receiving light from a point light source (110) and converting it into parallel light. Since the angle of refraction of the lens varies depending on the wavelength, it is preferable to use an aspherical lens or a compound lens tailored to the center wavelength. In this regard, it is also preferable that the light source (100) be a quasi-coherent light source based on monochromatic light as described above. This is because if white light is used as the incident light for the focusing lens (120), it is difficult to properly manufacture lenses according to the angle of refraction of each wavelength, which causes a problem of chromatic aberration.

[0021] The above polarizer (130) is intended to polarize the parallel light coming from the focusing lens (120) and send it into the optical space modulator (200). The parallel light (electromagnetic wave) incident on the polarizer (130) is an S-wave (vertical polarization, TE: Transverse Electric Field) perpendicular to the plane of incidence with respect to the electric field, or a P-wave (parallel) parallel to the plane of incidence <parallel>Only the polarization, TM: Transverse Magnetic Field) passes through. Through this, the precise polarization required by the optical space modulator (200) can be easily obtained.

[0022] According to the embodiment, polarization may be achieved by placing a PBS (Polarizer Beam Splitter) at the position of the beam splitter (160) described later instead of the polarizer (130), but it is difficult to obtain the precise polarization required by the optical space modulator (200).

[0023] The above-mentioned optical space modulator (200) refers to a Spatial Light Modulator (SLM), and generally consists of a cover glass, a transparent electrode, a liquid crystal layer, a mirror coating, an electrode array (pixel), and silicon-based control electronics. By applying a voltage between the transparent electrode and the electrode array of each pixel using the control electronics, the long axis direction of the liquid crystal located at the corresponding pixel is made to form a predetermined angle with the propagation direction of the polarized light incident through the cover glass, thereby creating and outputting various interference pattern light sources by giving a phase change due to the optical path difference caused by the change in refractive index. Conventionally, to create a moiré pattern using an analog method, a diffraction grating must be used, so there was a problem in that the diffraction grating had to be replaced with a different one to change the grating spacing for resolution adjustment. However, when using the optical space modulator (200) of the above embodiment, there is an advantage in that interference pattern light sources can be easily and diversely created electronically and digitally. For example, the incident light can be easily made into the interference pattern light source by modulating it by 90 degrees (converting the S wave into a P wave or the P wave into an S wave).

[0024] The above-mentioned imaging lens (210) serves to project light from the interference pattern light source of the optical space modulator (200) onto a desired target (220). Here, the target (220) may be a screen that forms an image with interference patterns, a CCD for verifying the image, etc. In the precision inspection device according to the above embodiment, the object serves as the subject, and by projecting interference patterns onto the subject to create a moiré pattern, a precision inspection of the shape, such as the thickness of the subject can be performed.

[0025] According to an embodiment, when an LED is used as the light source (100), a band filter (131) may be further provided between the focusing lens (120) and the polarizer (130), as shown in FIG. 2. At this time, the bandwidth may be the width of a frequency band corresponding to a predetermined line width (e.g., 20 to 40 nm) with the frequency of the center wavelength in the center.

[0026] According to the embodiment, light reflected by the optical mirror (140) may be incident directly on the optical space modulator (200), but as shown in FIG. 1, an aperture (150) and a light splitter (160) may be further provided between the optical mirror (140) and the optical space modulator (200). In this case, the aperture (150) and the light splitter (160) may be arranged so that light reflected from the optical mirror (140) passes through the aperture (150), and only a certain amount of light passes through the light splitter (160) and is incident on the optical space modulator (200). Additionally, light from the interference pattern light source of the optical space modulator (200) may be arranged so that it passes through the light splitter (160) and then passes through the imaging lens (210). Here, the beam splitter (160) can be in any form that simply reflects the light coming out of the aperture (150) as shown in FIG. 1 and transmits the light coming out of the optical space modulator (200). A Polarizer Beam Splitter (PBS) that can replace the polarizer (130) can be placed at the location of the beam splitter (160), but this is not desirable for the reasons mentioned above.

[0027] The present invention is applicable to precision inspection technology for components in various industrial fields (PCB substrates, TFT panels, microlenses, etc.) and is applicable to industrial inspection equipment using a moiré pattern inspection method based on an LED monochromatic light source.

[0028] Although the description has been explained with reference to the attached drawings, it is not limited to the attached drawings and the embodiments described above and can be applied and implemented in various ways. Explanation of the symbols

[0029] 100: Light source 110: Point light source 111: Optical fiber 120: Focusing lens 130: Polarizer 140: Optical mirror 150: Aperture 160: Optical separator 200: Optical space modulator 210: Imaging lens 220: Object (screen, CCD, subject, etc.)< / parallel>

Claims

Claim 1 Light source; an optical fiber that transmits light from the light source; a point light source formed at the end of the optical fiber; a focusing lens that converts the light from the point light source into uniform parallel light; a polarizer that polarizes the light passing through the focusing lens; an optical mirror that reflects the light polarized through the polarizer; and an optical space modulator that creates an interference pattern light source digitally by incidenting the light reflected by the optical mirror. The optical space modulator is configured to include an imaging lens that passes light emitted from the interference pattern light source, wherein the optical space modulator is composed of a cover glass, a transparent electrode, a liquid crystal layer, a mirror coating, an electrode array (pixel), and silicon-based control electronics; wherein the silicon-based control electronics are configured to cause the long axis direction of the liquid crystal located at the corresponding pixel to form a predetermined angle with the propagation direction of the polarized light incident through the cover glass by means of a voltage applied between the transparent electrode and the electrode array of each pixel, thereby providing a phase change due to the optical path difference according to the change in refractive index to output the interference pattern light source; wherein the light source is a quasi-coherent light source based on monochromatic light having a predetermined center wavelength, and the focusing lens is manufactured to match the center wavelength; and wherein the optical space modulator is configured to receive light polarized through the polarizer and provide a phase change due to the optical path difference according to the angle formed with the long axis direction of the liquid crystal to electronically output the interference pattern light source in a digital manner. Precision inspection device using moiré patterns. Claim 2 A precision inspection device using a digital moiré pattern, characterized in that, in claim 1, the light source is a monochromatic light-based quasi-coherent light source having a full width at half maximum (FWHM) of ±10 to 200 Å with respect to the center wavelength. Claim 3 A precision inspection device using a digital moiré pattern, characterized in that, in claim 2, the focusing lens is an aspherical lens or a compound lens aligned with the central wavelength. Claim 4 A precision inspection device using a digital moiré pattern according to claim 1, wherein the light source is an LED light source, and a band filter is further provided between the focusing lens and the polarizer to reduce DC noise of the LED light source. Claim 5 A precision inspection device using a digital moiré pattern, characterized in that, in any one of claims 1 to 4, an aperture and a light splitter are further provided between the optical mirror and the optical space modulator, and the aperture and the light splitter are each arranged such that light reflected from the optical mirror passes through the aperture, and only a certain amount of light passes through the light splitter and is incident on the optical space modulator, and light from the interference pattern light source passes through the light splitter and then passes through the imaging lens. Claim 6 A precision inspection device using a digital moiré pattern, characterized in that, in claim 5, the optical space modulator modulates the incident light by 90 degrees to form the interference pattern light source.

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